How do you build a raft slab?

What is the minimum depth of raft foundation?

The minimum thickness of raft foundation is 300mm.

What is a raft foundation slab?

A raft foundation is a reinforced concrete slab under the whole of a building or extension, ‘floating’ on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground.

Is raft slab better than waffle slab?

Waffle slabs are built on top of the ground and need great drainage and really hard ground for the life of the building. Raft slab footings are dug into the ground, have more perimeter stiffness and more tolerance to poor ground conditions than waffle slabs. … Poor site drainage is easily disguised.

How do you build a raft foundation manually?

The maximum settlement should generally be limited to the following values: Raft foundation on clay – 65 to 100 mm. Raft foundation on sand – 40 to 65 mm.

2) Soil line Method (Elastic Method) of Raft Foundation Design.

Soil Characteristics Ks(Kg/cm2)
1. Very Stiff 2 to <4 5.4
3. Hard 4 and over 10.8

How do you figure concrete for a raft foundation?

Calculation of volume of concrete for the column:

  1. Volume of Concrete = 0.6×0.4×3= 0.72m3
  2. Volume of Circular column = πr2 x 3 = 3.14 x 0.252 x3 = 0.58m3
  3. Volume of concrete = 1.2x1x0.1 = 0.12m3 Total volume of concrete required for footing= 0.32+0.12=0.44m3
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What type of soil is suitable for raft foundation?

Raft foundation is preferred when the clayey soil is compact and hard. Even strap foundation can also be used. Soft clayey sand is prone to expansion and shrinkage. They have a low bearing capacity and are unsuitable for footing and strap foundation.

Are raft foundations more expensive?

Raft foundations are relatively inexpensive and fast to put down, when compared with other types of foundation. Ground excavations are less onerous than for trench excavations, for example, and the foundation and floor slab can often be combined, giving significant savings on materials and time.

Is raft a code for foundation?

IS : 2809-1972· shall apply. 3.1 For satisfactory design and construction of a raft foundation.